Retainers have already been known for some time. They basically serve to fix the tooth position of a patient. That is, by means of a retainer a status quo is fixed with respect to the tooth position in order to prevent possible changes in the tooth position over time.
Particularly typical is the use of retainers in the course of a post-treatment of an orthodontic treatment. The latter involved an active influence on the tooth position of a patient, wherein by means of suitable devices forces are exerted to the teeth, such that they change their position or orientation over time. After such an orthodontic treatment is finished and the use of the respective device is completed the teeth tend to return to their former position. If no post-treatment is performed the result obtained by means of the active treatment will at least partially regress and consequently negate the active treatment.
Therefore, subsequently to the active treatment typically the use of a retainer is recommended which fixes the newly obtained tooth position. In order to achieve this, such retainers are connected to a plurality of teeth, wherein the retainer is adapted to receive forces produced due to a desired intrinsic mobility of a tooth and to distribute the forces to the remaining teeth. Thus, a movement of the tooth is prevented. Such retainers are known for example from DE 20 2012 004 419 U1 and DE 102 45 008 A1 wherein in the latter document a so-called “2-point retainer” is described, which is firmly connected with only two teeth.
In the known retainers it has proven to be particularly disadvantageous that a precise adaptation of the respective retainer to the individual contours of the teeth to be fixed on the one hand is very expensive and on the other hand is usually characterized by only low precision even in the case of careful handling by an experienced dental technician. This is mainly due to the production of today's known retainers, which are adapted to the shape of the respective dental impression in a manual process by bending a starting material—typically a metal strand. The precision of such a processing is naturally limited, wherein the finished retainer can have a distance in the order of a few millimeters from a tooth to be fixed. Then, in order to close this “gap” between retainer and tooth it is necessary to provide a correspondingly larger adhesive bond that reliably encloses the retainers despite of its great distance from the tooth and consequently connects the retainer to the teeth in a force-fitting manner. This is disadvantageous both for the wearing comfort of the retainer and its durability, because shear forces occur during chewing and acting on the retainer or its adhesive bond are the greater the more “attack surface” they provide in the oral cavity. This often results in that a retainer is detached locally and then has to be fixed again manually. Likewise, regularly a fracture of the retainer occurs.
Furthermore, the known retainers have the disadvantage that their purely passive effect can already be “activated” by minor accidental dislocations of the retainer. Thus, it regularly happens that a retainer in an interdental area, where it freely, that is unglued, extends from one tooth to the respective adjacent tooth, is accidentally bent, for example as a result of an interacting chewing force.
By bending the projected length of the retainer is locally reduced, which results in that the retainer from then on pulls the adjacent teeth to one another. That is, the retainer is changed by means of the unwanted deformation from a passive to an active element, which now no longer acts as a purely fixing element, but actively influences the tooth position. Such an influence, however, has to be avoided in any case, since the active dental treatment is typically already completed at the time of use of the retainer and further teeth movements are not desirable. If a deformation of a retainer occurs, it may even be necessary to completely replace it.
Another disadvantage of today's retainers is their fixing effect, which can be referred to as “interlocking”. This interlocking means that a retainer known in the art in fact achieves the desired stabilizing effect, however, it couples the teeth so strongly to each other, that any load acting locally on a tooth is substantially evenly distributed to all teeth. An independent movement in a sagittal direction is largely suppressed because of the retainer. The same applies to vertical movements and rotations of the teeth about their vertical axis. As a consequence the force impact due to external forces is decreased permanently for each individual tooth which has the consequence that the alveolar bone in which the teeth are anchored by their roots, is much less irritated than is the case without the retainer, i.e. under “natural conditions”. This irritation, however, is particularly important because it leads to a stimulation of the bone tissue, so that it will be preserved. If the irritation of the bone tissue is decreased, it degenerates. The decreasing force impact on each individual tooth has accordingly the consequence that the alveolar bone degenerates in the region of the “interlocked” teeth because the impact of external forces on the bone tissue locally decreases.
From the foregoing it is clear that two kinds of tooth movements have to be distinguished: on the one hand tooth migrations occur, which represent a continuous movement of the tooth back to a malposition, wherein said tooth migrations should be suppressed by the retainer. On the other hand teeth also have a certain intrinsic mobility due to which the teeth are movable in all directions within a certain margin (about 0.2 mm) in particular when chewing loads occur, wherein the teeth return to their initial position after the load is relieved. However, these intrinsic movements are extremely important because of the associated stimulation of the bone tissue and should be restricted as little as possible by a retainer.
From EP 1782748 A1 a retainer is known which is made from of a zirconium oxide, i.e. a ceramic material. Due to the fact that the zirconium oxide is not deformable the retainer is milled or ground from a block. Zirconium oxide is characterized by a high flexural strength and is therefore very rigid and unyielding. However, because of the risk of fracture inherent to the brittle ceramic material the known retainer is very thick-walled and voluminous. However, these characteristics of the known retainers result in the above-described disadvantage of “interlocking”, which restricts the movement of the teeth in the socket (tooth socket) and become non-physiological, which eventually leads to a degeneration of the bone tissue.